Cathode structure for indirectly heated narrow elongated emitting surfaces



Oct. '21, 1958 w. H. KOHL 2,

CATHODE STRUCTURE FOR INDIRECTLY HEATED NARROW ELONGATED EMITTING SURFACES I Filed June 6, 1956 IIIIIIIIIIIIIIII INVENTOR. WALTER H. KOHL AT TORNEKS United States Patent i r 2,857,543. n V CATHODE STRUCTURE FOR lNDlREC Y HEATED NARROW ELONGATED EMIT- TING SURFACES. I 1

Walter H. Kohl, Los Altos, Calif; assignor, by mesne 1 assignments, to the United States of America as repparticularly to a cathodestructure forindirectly heated narrow elongated emitting surfaces.

in special electron discharge devices an elongated cath- 5 ode is required which may be of the order of six to eight inches in length and of the order of 3 8 inch or more in effective diameter. For successful operation this long ribbon-like structure must be held firmly in place and not change its geometrical position when heated. Prior art efforts directed to elongated cathode mounts often involve the use of several ceramic spacers of complicated shape and entail costly grinding and forming operations as well as the danger of contaminants being present.

A principal object of the present invention is to provide a cathode structure of the shape described which will retain its position upon heating, be simple and easy to manufacture, and will be substantially free of contaminants.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

Fig. l is a greatly enlarged parallel perspective view of a preferred embodiment of the invention partially in cross section; and

Fig. 2 is a top plan view of the embodiment in Fig. l drawn to a smaller scale.

Reference is now made to the drawing wherein the numeral 2 indicates a base for the cathode assembly constituted, for example, by a block of copper. L-shaped brackets 4 and 6 conveniently of stainless steel are fixed to the cathode block 2 in my convenient manner as by brazing in dry hydrogen. These brackets serve to support a rod 8 which is undercut as at 10 to fit into a slot cut in the end bracket 4, thus permitting the rod to expand lengthwise while being fixed in position. The rod 8 is made of an insulating refractory material having adequate hot strength to support the structure and being free of contaminants. Sapphire rod has been found quite satisfactory. The cathode per se is supported by the sapphire rod in such a manner as to be free to slide 5 along it when heated. This can be accomplished conveniently by providing a tube of active cathode alloy gen erally indicated at 11 which circumscribes and is carried by the rod 8. The tube is double-walled on one side, being provided with an inner wall 12 and an outer wall 14 spaced from each other to provide a hollow chamber 16; Conveniently, but not necessarily, this tube structure is achieved by using a square nickel tube 18 to which is brazed a channel 20. The channel 20 can be made of any suitable material which will serve for a cathode and conveniently cathode nickel can be used. The outer surface of the wall 14 is coated with a suitable emissive coating 22 which can be applied by any one of the conventional methods such as spraying, painting, or by cataphoresis.

2,857,543 Patented Oct. 21, 1958 ICC;

the heater andcathode connections are brazed into the cathode block.v The cathode connection 32 prevents a longitudinal shift of the cathode of a rotation about its long axis while permitting it to expand freely along the sapphire rod.

The two sides of the channel 20 are painted with acid washed zirconium. hydride so that a continuous gettering :action is obtained during operation of the tube. This action occurs by virtue of the factthat the sides of the channel 20 are, of course, heated during operation of the electron tube and thereby bring the zirconium to the most efiicient temperature for the absorption of gases. From the foregoing it is seen that the present invention provides a novel structure for the operation of elongated cathodes where it would not be feasible to rely on the mechanical strength of the cathode base metal itself for support. Sapphire is ideally suited inasmuch as it has a very high melting point far beyond the temperature reached during processing or operation of the cathode, and also inasmuch as it is of utmost purity by virtue of the fact that sapphire rods are single crystals and thus do not contain any noticeable amount of impurities.

While a flat-sided cathode has been shown in the illustrated embodiment, it is within the scope of this invention to give the emitting surface any other geometrical contour that may be desirable. For more complicated geometrical shapes, it is conceivable that more than one sapphire rod can be used to advantage to support the structure either internally or externally.

Obviously many other modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A cathode assembly for electron discharge devices comprising a base, a plurality of supporting brackets fixed to the base, a sapphire rod supported by said brackets, cooperating means on said rod and a bracket adjacent one end of said rod for fixing the rod in position relative to. that bracket at the point of engagement with the bracket but permitting the rod to expand longitudinally, a tube of active cathode alloy circumscribing, in contact over its entire length with, and freely carried by said sapphire rod so as to be capable of longitudinal expansion throughout its length relative to and independently of said rod, said tube on one side being double-walled, the inner surface of the inner wall of this side being adjacent the sapphire rod and the outer surface of the outer wall of this side being coated with an emissive coating, said shift of the cathode tube or a rotation about its long axis while permitting it to expand freely along the sapphire rod.

2. A cathode assembly for electron discharge devices comprising a base, a plurality of supporting brackets fixed to said base, a rod supported by said brackets; means fixing said rod to one of said brackets to prevent bodily essa-54s displacement of said rod relative to said brackets but permitting relative slidingaof said rod at one end as it :undergoes thermally-induced gehangeseinalengthxan 1elon gated cathode carried byrs'aid, rod randtrinacontact throughout its entire length W1 lih SHldtFI'Od alonetzand miounted thereon free for expansion and z contractiomi along: its

' 3., cathode Lassembly fbr; eleeu on dischargedevices comprising a base, a plurality of supporting 'bi'ackets entire length I'eIafiYG'ftheEGtO'T-aS s'aidscathode undergoes athermallylinduced 'changesdnz-lengtm zand means'r-rigidly joining 'said cathode" U358; .tcfiminalufixedr in said base? for restraining said -'=cathode-1: against- :longitudinal shift; and against rotation re1ative to"said--:rod;;said mo'd-beingg made of an insulating; refractory: materialisubstantiallyefteefibf 1 contaminants and-having zhotistrength adequate to 'sup- 1 portsaid cathode.

at one end as it undergoes thermally-induced changes in' length; an elongated cathode carried by said rod alone and in contact throughout its entire length .with said rod and mounted thereon free forexpansion and contraction 1 throughout its entire length relative thereto as said cathode' ,undergoe's" thermally inducedt changes length; and means rigidlj joiningrsaid cathode toia terminal-"fixed in 9 said base for restraining said cathode againstlongitudinal shift and against rotation relative to said rod..

"References: Cited :in'th' ifileiof lthis patent .UNITED STATES PATENTS Werner .g July 10, 19:56

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,857,543 October 21, 1958 Walter H Kohl It is hereby certified that error of the above numbered patent requiring Patent should read as corrected below appears in the-printed specification correction and that the said Letters Column 1, line 47, for "my" read any column 2, line 12, for "of", second occurrence, read or column 3, line 5, strike out "alone" and insert the same after "rod" in line 4, same column,

Signed and sealed this 17th day of February 1959,

( SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ofliccr Commissioner of Patents 

